As a mechanical expert with years of experience in lawn care equipment, I've seen a variety of issues that can lead to a lawnmower starting and then dying. There are several potential causes for this behavior, and it's important to diagnose the problem correctly to ensure a proper fix. Let's go through some of the most common reasons why your lawnmower might be experiencing this issue.

1. Clogged Carburetor
The first and most common issue is a clogged carburetor. This problem often arises when fuel is left in the lawn mower for an extended period. Over time, the fuel can become sticky and deposit residue, which can clog the tiny passages in the carburetor. This can prevent the proper flow of fuel to the engine, causing it to stall shortly after starting. If you suspect a clogged carburetor, you should clean it with a carburetor cleaner. Be sure to follow the manufacturer's instructions for cleaning and reassembling the carburetor.

2. Fuel Quality
Another factor that can lead to a lawnmower starting and then dying is the quality of the fuel. Poor quality fuel or fuel that has been sitting for too long can lead to a buildup of varnish and other contaminants in the fuel system. This can also clog the carburetor or other fuel lines. Always use fresh, high-quality fuel and consider adding a fuel stabilizer if you store your lawnmower for an extended period.

3. Air Filter
A dirty or clogged air filter can also be a culprit. The engine needs a proper mix of air and fuel to run efficiently. If the air filter is dirty, it can restrict airflow to the engine, causing it to stall. Check the air filter and replace it if necessary.

4. Spark Plug
The spark plug is another critical component that can cause the engine to start and then stall. If the spark plug is old or fouled, it may not ignite the fuel-air mixture properly, leading to stalling. Inspect the spark plug for wear or buildup and replace it if needed.

5. Ignition System
Problems with the ignition system, such as a faulty ignition coil or a bad ignition switch, can also lead to starting issues. If the ignition system is not functioning correctly, it can prevent the spark plug from firing, causing the engine to stall.

6. Fuel Cap and Venting
Sometimes, a simple issue like a loose or damaged fuel cap can cause problems. The fuel cap ensures that the fuel tank is properly vented, allowing air to enter as fuel is consumed. If the cap is loose or not venting correctly, it can create a vacuum that prevents the engine from running.

7. Engine Timing
Incorrect engine timing can also cause a lawnmower to start and then stall. The timing must be precise for the engine to run smoothly. If the timing is off, it can cause the engine to misfire and stall.

8. Overheating
Overheating can be another reason for a lawnmower to start and then die. If the engine gets too hot, it can cause components to fail or the engine to shut down to prevent damage. Ensure that the cooling system is functioning properly and that there is no blockage in the cooling passages.

9. Governor Adjustment
Some lawnmowers have a governor that controls engine speed. If the governor is not adjusted correctly, it can cause the engine to stall. Check the governor settings and adjust them according to the manufacturer's specifications.

10. Mechanical Issues
Lastly, there could be mechanical issues such as a seized engine component or a broken belt. These issues can prevent the engine from running smoothly and may cause it to stall.

In conclusion, diagnosing why a lawnmower starts and then dies involves checking several key components. Start with the most common issues like the carburetor and fuel quality, and then move on to other potential problems like the air filter, spark plug, and ignition system. Remember to always refer to your lawnmower's user manual for specific instructions and safety guidelines.

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The carburetor might be clogged. A clogged carburetor is most commonly caused by leaving fuel in the lawn mower for a long period of time. ... This sticky fuel can clog up the carburetor and cause the engine to stall. If the carburetor is clogged, try cleaning it with carburetor cleaner.read more >>